This invention relates to the interconnection of electronic components such as for example integrated circuit (IC) chips, chip carriers, printed circuit boards and, in particular, to methods of forming an interconnection wire on a contact on an electronic component, methods of interconnecting contacts on first and second electronic components, a bonding head for a wire bonder and electronic components per se.
As the size of electronic components is reduced due to advances in the techniques by which they are manufactured, the density with which such components can be arranged in a piece of equipment becomes increasingly dependent on the space required to form interconnections to contacts on the components. A commonly used technique involves fastening a component such as an IC chip to a substrate such as a printed circuit board by means of an adhesive. Interconnection wires are each bonded at one end to a respective contact on the component by thermocompression wire bonding (which uses a combination of heat and pressure to form a weld), and are bonded at or towards their other end to a respective contact on the substrate, again generally by thermocompression wire bonding. A significant disadvantage of this technique is that the area occupied by the installed component with its interconnnections is significantly greater than the area of the component itself. The configuration of an interconnection made by this technique will be as disclosed in U.S.Pat No. 4,417,392.
An interconnection technique which reduces the space required to form the interconnections to a component involves the formation of "bumps" of a conductive material on the contacts of either the component or the substrate to which the component is to be connected. The bumps allow connections to be made between the contacts on the component and contacts on the substrate which are directly opposite the component contacts. Generally, the bumps comprise a solder material and are applied to contacts by plating. Connection of a bump to a second contact can then be achieved by reflowing the solder. It is also known to form bumps by forming a bond between a ball on the end of a length of wire and a contact by thermocompression wire bonding, and breaking the wire immediately above the ball. A connection between the ball and a second contact can then be made by means of a welding technique such as ultrasonic bonding. This technique is disclosed in JP-A No. 59.208751, JP-A No. 60.089951 and JP-A No. 60.134444.
Interconnections between electronic components which are formed by means of bumps suffer from the disadvantage that frequently they are not sufficiently compliant to withstand forces exerted on thermal cycling, which can result in differential expansion of the components and breakage of at least some of the interconnections.
U.S. Pat. No. 3,373,481 discloses a technique for securing conductive pedestals to terminal elements of an integrated circuit device, which comprises thermocompression bonding gold spheres onto the terminals using a tool which, deforms the spheres into elongate pedestals. The pedestals are connected to interconnect areas on a printed circuit board by means of a solder in which the gold of the pedestals dissolves. The application of this technique to densely packed contacts is limited by the accuracy with which the tool used to deform the spheres can be manufactured. Furthermore, the disclosed technique relies on dissolution of the material of the pedestals in order to ensure that they are of approximately equal height and therefore that interconnections can be made between all of the pedestals and respective contacts which lie in a single plane. This has the disadvantage that the resulting joint between the pedestals and the solder is embrittled on dissolution in the solder and, moreover, if it is desirable or necessary to break the solder connections and subsequently to remake them (for example for repair), the length of pedestal remaining for such subsequent connection is reduced.